Results of Phase II research indicate that formal validation of the EpiAirway? in vitro human bronchial tissue model for predicting toxicity of inhaled chemicals is an attainable goal. The proposed Phase IIB cooperative agreement project is intended to realize this goal by conducting formal ring trial validation studies that will be submitted to regulatory agencies and the Organization for Economic Co-operation and Development (OECD) in support of formal adoption for regulatory use. Aim 1 will develop the final validation plan in collaboration with an NIH Steering Committee (SC). In Aim 2, an expanded of set 75 chemicals will be tested in the lead project laboratory to verify the accuracy and relevance of the final prediction model. In Aim 3, training of the participating ring trial testing laboratories will occur. In Aim 4 the transferability, reproducibility, accuracy and relevance of the EpiAirway? model and protocols will be established by conducting formal ring trials in 3 GLP compliant contract research laboratories. Preparing a final report of all study activities and submission of the study data to relevant US regulatory agencies and the OECD in support of adoption as a test guideline for regulatory use will be the goal of aim 5. The technology to be validated in the current Phase IIB proposal will be the first non-animal model for use in regulatory inhalation toxicity testing. Successful completion of the Phase II project will address a critical barrier to implementation of worldwide requirements for inhalation toxicity testing of chemicals, and provide a technical capability that is urgently needed but that does not presently exist. The validated model and testing protocol will be utilized worldwide by a wide variety of chemical manufacturers, consumer product manufacturers and industries which utilize chemicals to produce other products. Specific US federal agencies that may adopt and accept results of the validated test system include the Consumer Product Safety Commission (CPSC), the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA). The European Chemicals Agency (ECHA) will also be able to utilize data produced by the validated test system in support of hazard assessment in EU countries. Formal validation and adoption of the EpiAirway? model and test system will generate commercial sales resulting from direct utilization by chemical manufacturers, consumer product manufacturers and regulatory agencies. Additional revenue will be generated by offering the EpiAirway? Respiratory Toxicity test as a contract service that may be offered by numerous contract testing laboratories, including MatTek Corporation.